The present invention is generally directed to fuel cell components and more specifically to fuel cells configured for direct internal reforming.
In a high temperature fuel cell system, such as a solid oxide fuel cell (SOFC) system, an oxidizing flow is passed through the cathode side of the fuel cell while a fuel flow is passed through the anode side of the fuel cell. The oxidizing flow is typically air, while the fuel flow is a hydrocarbon fuel, such as methane, natural gas, pentane, ethanol, methanol, etc. The fuel cell, operating at a typical temperature between 750° C. and 950° C., enables the transport of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the ion combines with either free hydrogen or hydrogen in a hydrocarbon molecule to form water vapor and/or with carbon monoxide to form carbon dioxide. The excess electrons from the negatively charged ion are routed back to the cathode side of the fuel cell through an electrical circuit completed between anode and cathode, resulting in an electrical current flow through the circuit.
As the solid oxide fuel cell technology progresses towards commercialization, the demand for higher power densities will lead to making SOFC systems more cost effective. This demand for higher power densities will cause elevated temperatures in the fuel cell stack. If this heat is not controlled, the interconnects of the fuel cell could melt.
Direct internal reforming of a hydrocarbon fuel to a hydrogen containing fuel within the stack at the SOFC anode (i.e., fuel) electrode is an effective way of cooling the fuel cell reaction site. In this type of reforming, an unreformed hydrocarbon fuel is provided to the anode to be reformed to a free hydrogen containing fuel, and an external reformer may be omitted. However, the reforming reaction at the anode electrode causes high localized thermal stresses. The traditional nickel based anodes are very reactive in the CH4 reforming reaction at the temperatures under which the SOFC operates. The tendency is for the reforming reaction to take place very quickly upon entering the anode flow field, causing severe and in some cases catastrophic temperature gradients which could lead to fuel cell failure.